JAKARTA, Indonesia_Four years ago, young pilots lined up to join a new contender in Indonesia's booming aviation industry. But at least 20 left Adam Air within months, citing concerns that poor maintenance, corruption and rule-bending could lead to a crash - charges the airline denied.

"I didn't want to wait until I had lost my friends," said Feisal Banser, 30, a former Adam Air flight captain who knew several crew members on a passenger jet that crashed Jan. 1 with 102 people on board.

Adam Air, founded by Agung Laksono, the speaker of the House of Representatives, is one of dozens of privately held airlines to have emerged since Indonesia started deregulating the industry in the late 1990s, bringing cheap air travel to the sprawling island nation.

Experts say there is no evidence budget airlines are less safe than full-fare competitors, but the rapid expansion of the sector has raised concerns that, in Indonesia at least, growth has outpaced the supply of trained aviation professionals, regulatory oversight, parts and ground infrastructure.

"The industry growth is so fast and it's not matched by the growth of human resources," said Dudi Sudibyo, an aviation expert called on to advise President Bambang Susilo Yudhoyono about Adam Air Flight KI-574, which disappeared on New Year's Day during what was supposed to be a short hop between islands.

"There are not enough regulators, flight inspectors or planes," he told The Associated Press.

The Adam Air pilot did not issue a Mayday before his plane fell off the radar in severe winds and with the flight data recorder still missing, experts do not know yet what happened.

But the crash off Sulawesi Island's western coast - 16 months after a domestic Mandala Airlines passenger jet slammed into a bustling neighborhood on takeoff, killing at least 149 people - put the spotlight back on the aviation industry.

Adam Air has a fleet of 17 aircraft that fly to popular tourist destinations like the resort island of Bali and the country's cultural hub of Yogyakarta, as wells as routes to Singapore and Malaysia.

Sutan Salahuddin was among 17 pilots who jointly resigned from Adam Air in May 2005 citing alleged safety concerns. They are now being sued by the airline, which alleges they violated their contracts and owe the company training fees, according to the West Jakarta District Court, which is expected to issue a ruling within weeks.

The demand for pilots with ratings for jets such as the widely used Boeing 737-400 is so great in Indonesia that companies often poach them from each other, sparking lawsuits to recover training costs.

Banser and Salahuddin alleged that as part of efforts to save costs, parts were replaced or recycled, regulatory officials were bribed, or pilots were pressured to break international safety regulations.

Salahuddin, who joined Adam Air at its inception, says he left after essential problems with his plane's inertial reference unit, a key navigational tool, were repeatedly left unfixed.

"I saw how Adam Air managed the maintenance of the aircraft and I resigned to protect my life and the life of the passengers," the 35-year-old said, adding that he was once asked by the company's operations chief to sign documents clearing a flight because there was no technical engineer at the airport.

"He called me in the cockpit and told me to fly, but the aircraft was not airworthy," said Salahuddin who refused to take off, enraging his managers.

Adam Air's director of safety and security, Capt. Hartono, denied the allegations and all others claiming that the company knowingly violated international safety guidelines.

"These are just rumors," he said, refusing to comment further.

No other officials from the airline could be reached, several employees are believed to have changed their phone numbers since last week's disaster, and large sections of corporate information on Adam Air's Web site have been removed.

The Center for Transportation and Logistics Studies, a private policy group, said Indonesia's discount airlines have increased the amount of time planes spend in the air, from 70 percent to up to 95 percent to boost profit margins, putting a crunch on servicing.

But there is not enough data available to say if that was jeopardizing safety, said Danang Parikesit, a leading researcher, though cost-cutting was "probably reducing the safety standard."

Bansar, one of the former pilots, said there was no doubt in his mind that was the case.

When mandatory aircraft part replacements were due, including essential navigational instruments, Adam Air officials "swapped with another aircraft, so as not to replace it ... then if they didn't find the part for another 30 days, they would swap it again," he claimed.

Banser said he flew on a plane with a cracked door handle "for several months" because there was no spare in stock. He asked an engineer if it was legal to fly with the defect and "he just smiled."

"Every time you flew, you had to fight with the ground staff and the management about all the regulations you had to violate," said Banser, who says he was grounded for a week in 2005 after refusing to fly because he would exceed the maximum of five daily takeoffs.

He said he gave in to demands that he fly the plane - which also had a damaged window - after managers agreed to pay each crew member an additional million rupiah (US$110) - an offer Bansar accepted.

But eventually the pilot said he lost faith and quit.

Sudibyo, the aviation expert advising Yudhoyono, recalled a still-unexplained incident last year when one of its Boeing 737s went missing for hours following a navigation and communications breakdown, eventually making an emergency landing in Tambolaka, hundreds of kilometers (miles) from its final destination.

The airline broke several civil aviation regulations that day, including flying the plane away from the scene before an inspection by aviation authorities, he said. The pilot was fired, but government regulators would not say if the airline was fined, citing confidentiality regulations.

"The safety report on that company is a big question mark," Sudibyo said.

Iksan Tatang, Indonesia's top civil aviation official, said he had heard about the accusations, but could not respond in detail until reviewing formal complaints from the pilots.

"I invite the pilots to give me the information. Why did they give it to everybody, but not the regulators?" he asked. "As far as I know, we have to follow the international regulations."

Pilots said they regularly reported maintenance problems to technical staff, but were grounded or docked pay when they confronted managers. Filings on aviation incidents are confidential and several officials said they were unaware of any company ever having been held criminally libel in a fatal Indonesia transportation accident.